This invention generally relates to a portable water purifier for purifying and storing drinking water, and more particularly to a purifier positionable on an existing conventional water cooling and dispensing unit.
Concern over drinking water purity and taste have prompted alternative sources of supply other than that supplied by processed tap water. This concern has been fueled by widely publicized reports of water pollution and by tap water often containing large amounts of water treatment chemicals, minerals and other matter.
One attempt to deal with this problem is the increased use of bottled waters. Sales of bottled waters which have increased substantially in recent years generally consists of a single serving to a one gallon container sold in retail establishments, and of larger containers, e.g., 5 gallon containers, sold for use with water cooler dispensers. Bottled cool water dispensers are extremely popular for both residential and commercial use because cold drinking water may be dispensed from generally a three to five gallon bottle without the need for plumbing. However, such bottled waters are expensive, and changing and storing large heavy and cumbersome bottles is burdensome.
Several problems with the quality of bottled waters also have been discovered and publicized in recent years. Bottled waters can readily become contaminated by airborne bacteria and viruses during the dispensing operation by the introduction of ambient air drawn inside the bottle as the water is dispensed. Further, the stagnant storage of bottled water allows bacteria to grow unchecked. Discoveries of dangerous chemicals and extremely high levels of bacteria in bottled waters has led many to the conclusion that bottled water may be no more pure, or sometimes even less pure, than ordinary tap water. Such problems with tap and bottled water have revealed a need and desire for water treatment at the point of use.
Several point of use treatment alternatives exist to tap and bottled water and are well known in the art. One such alternative is the use of carbon filtration which use activated charcoal to remove impurities, consisting mostly of organic compounds, and to improve the taste of water. Carbon filters, however, are generally ineffective in removing most inorganic compounds such as lead and arsenic.
Another alternative known in the art is the use of reverse osmosis to treat the water. Reverse osmosis units use a sediment prefilter. These units however, have a tendency to become clogged by high levels of hardness minerals and thus are not feasible for some geographic locations. Other problems with reverse osmosis include the waste of approximately 80% of the feedwater, the great expense of replacement membranes and the requirement of pressurized water feed lines and water drain lines which eliminates portability.
Another alternative point of use water treatment method is distillation. Distillation devices purify water by boiling water to generate steam, and then condense the steam to form water free from such contaminants. The contaminants having a vaporization temperature higher than that of water remain in the boiler, while solvents which have a boiling point lower than water may be separated from the steam by venting before condensation. The distillation process is more effective in removing impurities than reverse osmosis and does not have the problem of water waste.
Distillation devices may be portable, without the need for pressurized feed lines and drain lines or non-portable which require feed lines to supply water. Distillation alone, however, is relatively ineffective in removing volatile chemicals such as benzene and chlorine.
Existing portable distillers and most non-portable devices have failed to adequately deal with the problem of scale deposits in, and cleaning of, the boiler, as for example, the portable distillation device shown in U.S. Pat. No. 4,342,623 which has no provision to inhibit scale build-up. Other prior art portable distillation devices have a removable boiler, but require partial disassembly of the unit for removal of the boiler. Additionally, most of the known distillation units include a float valve within the boiler, such as U.S. Pat. No. 4,943,353 and is thus exposed to the build-up of scale. When excessive scale deposits occur failure of the float valve may result which may cause an overheating situation and a system failure. Other distillation units, such as in U.S. Pat. No. 5,178,734, may have an external solenoid valve controlled by level probes within the boiler. The probes are thus exposed to scale build-up.
Distillation units in the prior art are of the type wherein the water is distilled and captured for subsequent use, such as illustrated in U.S. Pat. No. 4,342,623; of the type wherein uncooled water may be dispensed as illustrated in U.S. Pat. No. 4,622,102; or of the type wherein the distillation unit is coupled with refrigeration such as illustrated in U.S. Pat. No. 3,055,810. As aforesaid, bottled water dispensers are extremely popular. It is thus advantageous to replace the water bottles of such containers with a less expensive and purer water source such as an efficient distillation unit.
In U.S. Pat. No. 5,281,309, assigned to the common assignee of the present invention, a water purification apparatus is disclosed which is mounted within a housing adapted to be positioned on a conventional water cooler/dispenser. The apparatus includes a valve control member which extends from the housing and is positionable within the water reservoir of the dispenser to control the release of purified water from the apparatus to the reservoir. To provide a compact housing for the water purification apparatus a boiler having a small cross section was provided in order to provide a high energy heating element in the boiler the length of the boiler was extended to prevent the water in the boiler from surging or flash vaporizing upwardly into the condenser coil, a condition known as "carry-over" the boiler disclosed in the aforesaid patent application was extended. Additionally, the level of the water within the boiler was controlled by the water level in the feedwater tank which is at an upper portion of the apparatus so that the height of the boiler had to be great enough to prevent water within the boiler from flowing or flashing into the condenser. In copending U.S. patent application No. 08/136,449 filed Oct. 14, 1983, also assigned to the common assignee of the present application, a baffle was placed above the heating element in the boiler to preclude carry-over, and a separate water level control tank was positioned between the feedwater tank and the boiler so the water level in the boiler could remain independent of the level of water in the feedwater tank.
A significant difficulty addressed by the present invention is the foaming that occurs with all known distillation apparatus incorporating high energy heating elements into small boilers. The foaming that occurs in water distillation apparatus creates the problem of contaminants being carried by the foam into the condenser unit coil and this results in contamination of the distilled water. Although anti-foaming agents are widely used in the food industry and are metered by elaborate metering pumps, such agents have not been used in compact distillation apparatus. One reason for this may be because heat from the boiler breaks down the foaming agent so the foaming agent has to be applied continuously in a very diluted form which would have required an elaborate diluting and metering system. Metering systems in this environment would be excessively expensive and not be cost effective. The present invention provides an effective and economical solution to this problem.
The steam which is formed in the boiler flows into a condenser where it is cooled and condensed into contaminant free water. The condenser generally is a helical coil having a number of convolutions and having external fins for providing a large heat transfer surface area for receiving heat from the coils by conduction. Cooling air is forced over the fins to receive energy from the fins by convection. In the prior art water purification apparatus the flow of cooling air has been through the center of the-helical coil. The air thus contacts the portions of the fins bordering only along the central path. To increase the heat transfer efficiency, a globe or similar device has been mounted in the center of the coil to place frictional resistance in the central portions so that the air is directed between the exterior of the globe and the fins. However, even with this construction, only a small portion of the air flows across the entire surface of the fins. If the air could be directed entirely over the fins, the coil could be shortened substantially. The present invention addresses and provides a solution to this problem.
Another problem with the prior art to which the present invention is directed is the manner of securely mounting the boiler within the housing of the housing of the apparatus. Generally a connecting member such as a bolt or a rod extends through at least one end of the boiler to fasten the boiler to a portion of the housing. Not only does such a construction require a seal about the connecting member which functions properly at elevated temperatures, but also since a portion of the connecting member is within the boiler it is subjected to the corrosive action of the heated water and steam and to scale build-up. Under such circumstances, disassembly of the boiler when required may present difficulties.